In recent years, with growing concern about global warming, the need for reduction in power consumption of home electric appliances has been widely recognized. Among home electric appliances, refrigerators in particular are products which consume much electric energy and therefore reduction in power consumption of refrigerators is indispensable to counter global warming. Since power consumption of a refrigerator, when the load in the refrigerator is constant, largely depends on the efficiency of an internal cooling compressor and the heat insulation performance of a heat insulating material associated with heat leakage from the inside of the refrigerator, it is important in refrigerator technological development to improve the compressor efficiency and the heat insulating material performance. As examples of the prior art for improving heat insulation performance, conventional vacuum heat insulating materials will be discussed next.
A vacuum heat insulating material uses a getter material to maintain the vacuum on the inside.
For example, Patent Document 1 (Japanese Patent Laid-Open No. 2004-3534) describes a vacuum insulating material in which a recess is made to house a getter material in the junction face of at least one of core material boards made by heating and pressure-forming an inorganic fiber material, in order to prevent a protrusion generated by the injected getter material from breaking the vacuum heat insulating material.
Patent Document 2 (Japanese Patent Laid-Open No. 2002-48466) describes a technique that a foam insulating material and a vacuum insulating material lie in space composed of an outer case and an inner case where the vacuum insulating material is composed of a getter material absorbing moisture and an envelope made of gas-barrier film, and the getter material is held unmovable between molded sheets of core material inorganic fiber without using any fixing member or any fixing structure such as a housing recess so that the adsorbent is held fixed in place during a vacuum insulating material manufacturing process such as an evacuation process and cost reduction is thus achieved.
Patent Document 3 (Japanese Patent Laid-Open No. 2004-218747) describes a vacuum insulating material composed of a core material, a getter material and an envelope wrapping them wherein the getter material is placed in a recess provided in the core material and the envelope facing the getter material is a laminate film having an aluminum foil layer, with a pierce-proof protective sheet between the getter material and the envelope, thereby preventing generation of pinholes during vacuum sealing.
The vacuum insulating material described in Patent Document 4 (Japanese Patent Laid-Open No. H4 (1992)-337195) includes a housing member whose inside is vacuum, an inorganic fiber mat lying in the housing member, and an inner film bag which temporarily compresses the inorganic fiber mat to prevent the vacuum insulating material from wrinkling, warping or bending.
It is known that, in order to prevent moisture or a gas component from the core material used in the vacuum insulating material from lowering a high degree of vacuum, a step of drying the core material or a similar step is taken to remove moisture and gas components from the core material before an evacuation step. It is also well known that a getter material such as synthetic zeolite or activated carbon is placed in the vacuum insulating material in order to absorb traces of moisture or gas components which would be generated from the core material when the core material is stored in a high degree of vacuum for a long time. Therefore, the core material from which moisture and gas components have been removed by a drying process, etc. must be immediately placed in a vacuum condition in which there are no moisture and gas components so that it does not absorb moisture or gas components from outside again.
However, in case of the above conventional techniques described in Patent Documents 1 to 3, the getter material is housed between plural core material boards and covered by plural sheets and thus a process of embedding the getter material is needed to house and hold in place the getter material or cover it with a protective sheet. During the embedding process, there is a possibility that the core material boards may absorb moisture or gas components in the atmospheric air.
Next, this problem will be explained referring to FIG. 13. FIG. 13 is a sectional view showing the structure of a conventional vacuum insulating material. In the figure, a vacuum insulating material 1 is composed of core members 2a and 2b, an envelope 3 and a getter material 4. A recess 5a is formed almost in the center of the plane of junction between the core members 2a and 2b and the getter material 4 is contained in this recess 5a. Therefore, for the getter material 4 to be placed between the core members, the core member 2b must be lifted to place the getter material in the recess 5a or the getter material must first be placed in the recess 5a of the core member 2a alone before the core member 2b is laid to cover the getter material 4. This means that working time is required to embed the getter material in this way and during such embedding work, the core member 2a or 2b may absorb moisture or gas components in the atmospheric air.
Besides, when a core material is used inside heat insulating walls of a refrigerator, etc, it may be necessary to prepare core material members of different sizes depending on the size of the refrigerator, etc. or the size or thickness of the heat insulating wall. This implies that core members must be stored in the course of manufacturing until all core members of required sizes are prepared. However, since core members after a drying process must be immediately stored under a vacuum in a dry space or the like in which there is no or the least moisture, in order to prevent the core members from absorbing moisture or gas components from outside (in the atmospheric air) and consequently the working process is very tight in terms of time. However, the above patent documents do not suggest any concrete measure to solve this problem.
Patent Document 4 does not suggest any concrete measure to prevent adhesion of moisture or gas components from outside to the inorganic fiber mat in the housing member.
The present invention has been made in order to solve the above problems inherent to the prior art and one object of the invention is to reduce absorption of moisture or gas components by a core material during storage in the course of manufacture. Another object of the invention is to provide a vacuum insulating material which improves the manufacturing efficiency and maintains and improves the heat insulation performance.